Is It Acceptable to Deviate from IPC Standards?
Standards should enhance, not hinder, a design.
Why are all the guidelines slightly different? Should all designs follow IPC standards?
The answer is simple: Every board is a new creation in the universe. The board design represents the technology needed, the designer’s preferences, and the engineer’s preferences mixed with cost considerations. The standards are in place to guide designers, fabrication and assembly in a uniformed path.
IPC standards permit design, fab and assembly to communicate in easier terms. Once one party states the class, then all parties have an idea of the requirements for their respective processes. The processes of the different parties drive the decisions made to achieve the desired class of fabrication and assembly. Cost and schedule are impacted by the class.
Deviations are required at times to complete the layout. In a particular layout I was involved in, Class 3 was not possible within a 0.8mm BGA. The component could not be changed, and the customer required Class 3. Eventually, the customer allowed a deviation in the BGA area. The deviation was to permit the BGA area to be Class 2, while the remainder of the board was Class 3. This was several years ago, but it remains a good example when explaining the requirement to understand the IPC class structure.
Technology tends to outpace documentation. New components push the barrier of fabrication technology. IPC standards typically are not updated until the process becomes common and repeatable; therefore, there will be times when IPC rules cannot be followed. In these cases, I stay as close to IPC specs as possible, then verify my decisions with assembly and fabrication shops.
Should you follow IPC standards? As much as possible, but do not let the standards block a solution.
Figure 1. Board cost is tied to the class specified, but deviations are allowed – and can save money.
is president and CEO of ACD (acdusa.com); This email address is being protected from spambots. You need JavaScript enabled to view it.. His column runs bimonthly. He is speaking on Design for High-Reliability Assembly at PCB West in September.
